This invention relates to electrically conductive grounding straps that are used to discharge static electricity from personnel handling sensitive electronic components, and more particularly to apparatus for monitoring the integrity of the connection between the grounding strap and a known electrical ground.
Electrically conductive grounding straps are used to provide a path to ground for dissipating static charges on personnel. Such devices are integral elements of electronic workstations, protecting sensitive electronic components from degradation or destruction caused by electrostatic discharge. An example of such a grounding strap (often referred to as "wrist straps" since they are generally worn around a person's wrist) is disclosed in U.S. Pat. No. 4,475,141 entitled "Body Electrical Grounding Tether" and issued on Oct. 2, 1984. Such wrist straps consist of a lightweight elastic band and a ground lead with a plug or clip for connecting the lead to a known electrical ground.
The electrostatic discharge which such wrist straps are intended to dissipate can be on the order of several thousand volts of electrostatic build-up. Such charge is generated through normal movements of personnel. For example, static charge can be built up by walking across a carpet in a low-humidity environment. The use of wrist straps to drain potentially harmful charges away is a good approach, but standing alone has a major flaw; namely, there is no way to know if the wrist strap is functioning properly. Thus, if the wrist strap is improperly worn by personnel, or if there is cord breakage, any bad connection, or loss of continuity, failure of the charge dissipation would occur and might not be discovered until costly damage to delicate electronic circuitry has already occurred.
It would be advantageous to provide apparatus for detecting any open circuit between the user of a wrist strap and ground. Should such a situation develop, an audio and/or video indicator would be useful for informing the user that a problem exists which must immediately be remedied.
It would be further advantageous if such a wrist strap monitoring apparatus were built into the wrist strap itself, and also monitored the condition of the grounding cable for any fault. Such design would be convenient and ensure that the monitor is always in use and working while the wrist strap is being worn. It would be further advantageous if such monitoring apparatus and wrist strap were packaged together with a wristwatch for convenience in use by applicable personnel.
The present invention relates to such a wrist strap and integral ground monitor.